Recurrent infections with herpes simplex viruses (HSV) are a significant clinical problem. Fundamental to understanding the nature of recurrent herpetic disease is determining precisely how HSV alternates between the two phases of its dual life cycle, latency and reactivation of productive infection. The LAT-ICP0 locus plays a central role in the regulation of HSV- 1 latency and reactivation. The genes that encode for the latency-associated transcripts (LATs) and infected cell polypeptide 0 (ICP0) form a continuous locus in the repeated regions of the HSV genome. Specifically, the LAT and ICP0 genes lie on opposite strands of HSV-1's double-stranded DNA genome and share a significant overlap. Thus, the abundant LATs can hybridize to 0.75 kilobases of complementary sequence in ICP0 mRNA. While the antisense arrangement of the LAT-ICP0 locus has long been recognized, the hypothesis that LAT RNAs serve as "antisense repressors" of ICP0 gene expression has not been rigorously analyzed. The juxtaposition of the LAT and ICP0 genes mirrors their opposing roles in latency. While LAT RNAs facilitate the maintenance of HSV latency, expression of ICP0 is necessary and sufficient to induce HSV-1 reactivation. Conversely, failure to express ICP0 is highly conducive to HSV genomes entering a transcriptionally repressed state. Thus, antisense repression of ICP0 mRNA translation is one mechanism by which LATs may facilitate the maintenance of latency. The goal of this research proposal is to evaluate the concept that LAT RNAs and ICP0 form a pair of mutually dependent, opposite regulators that are the yin and yang of HSV latency. Specifically, genetic evidence will be obtained to test the hypothesis that "All viral proteins that induce HSV-1 reactivation in the trigeminal ganglion cell culture model achieve this phenotype via (a) induction of ICP0, (b) suppression of LAT transcription, or (c) both."